1. Field of the Invention
The present invention relates to a primary radiator for use in a beam scanning antenna in the microwave or millimeter wave band, and more particularly to a primary radiator capable of moving an electromagnetic wave output part in a two dimensional plane without causing unwanted leakage of a high frequency signal, and a phase shifter and beam scanning antenna using the same.
2. Description of the Related Art
A variety of beam scanning antennas using electromagnetic beams in the microwave or millimeter wave band have been proposed in the prior art. There are two major methods of beam scanning: mechanical beam scanning and electronic beam scanning.
In the mechanical beam scanning method, beam scanning is performed by moving a portion of an antenna that has a given directionality or by moving the entire antenna. According to this method, the construction is simple because usually one antenna is moved to scan one beam. However, the provision of the mechanical movement involves the problem that high speed beam scanning is difficult in the case of a large antenna.
The electronic beam scanning is classified into two types: one that uses an array antenna constructed from an array of antenna elements and scans the beam by controlling the phases of the high frequency signals fed to the respective elements by means of phase shifters, and the other that uses a plurality of antennas having different directionalities and scans the beam by switching among them by means of switches. These types of beam scanning can accomplish high speed beam scanning because they do not require the provision of mechanical movements, but the problem is that the phase shifters and the switches are expensive, limiting the use of these types of antennas.
Latching ferrite phase shifter are commonly used as the phase shifters for electronic beam scanning type antennas. Since this type of phase shifter usually controls the phase in eight steps, i.e., in increments of 45 degrees, there arises the problem that, with this type, the phase cannot be controlled continuously. It is also said that this type of phase shifter has the problem that the response time is slow compared with the switch.
On the other hand, PIN diodes are commonly used as the switches for switching among the antennas. However, the PIN diode is a switch that switches between open and closed states, and therefore has the problem of large insertion loss. Another problem is high cost, because as many switches are required as there are antennas.
In recent years, with advances in semiconductor fabrication technology, phase shifters and switches have begun to be fabricated in MMIC (Microwave Monolithic Integrated Circuit) form, promising to increase the performance of beam scanning antennas, but since the MMIC is also expensive, there is a need to provide an inexpensive phase shifter that can control the phase.
In view of this, the applicant has proposed in Japanese Unexamined Patent Publication JP-A 2001-127524 (2001) a beam scanning antenna comprising a primary radiator placed between two parallel metal plates, a wave collector constructed from a dielectric lens or a reflector or the like, and a plurality of slots formed in one of the parallel plates. According to this beam scanning antenna, a high frequency spherical wave signal radiated from the primary radiator propagates through the space between the parallel plates, and is converted into a plane wave by the wave collector. Further, the positional relationship between the primary radiator and the wave collector is varied and, using this as a phase shifter, the tilting of the electromagnetic wave phase can be controlled. The beam can be scanned by externally radiating the high frequency signal, whose phase has been controlled by the phase shifter, directly through the slots formed in one of the parallel plates, or by feeding the high frequency signal to another antenna element mounted outside the slots. This beam scanning antenna can be fabricated at low cost because it is constructed using the parallel plates, the wave collector forming the phase shifter, and the primary radiator.
The beam scanning antenna proposed in JP-A 2001-127524 by the applicant requires that either the wave collector or the primary radiator or both be moved to vary the positional relationship between the wave collector and the primary radiator. Both the wave collector and the primary radiator are placed between the parallel plates, and the high frequency spherical wave signal radiated from the primary radiator, after being converted into the plane wave by the wave collector, is fed to the slots acting as radiating elements or feed windows to the outside. Therefore, to allow the wave collector or the primary radiator to move, a prescribed gap must be provided between each parallel plate and the wave collector or the primary radiator.
However, when a gap is provided between each parallel plate and the wave collector, the sum of the high frequency signal converted into the plane wave by the wave collector and the high frequency spherical wave signal passed unchanged through the gap between each parallel plate and the wave collector is fed to the slots. In this case, the spherical wave and the plane wave arrive out of phase at the slot feed point; as a result, in some instances, the phase of the high frequency signal fed to the slots may be disturbed.
On the other hand, when a gap is provided between each parallel plate and the primary radiator, since the wave source consists only of the primary radiator which has directionality, the phase is relatively unaffected. However, a high frequency transmitter/receiver is usually connected to the primary radiator, and the transmitter/receiver is a precision component and relatively large in weight; hence the problem that moving the primary radiator for beam scanning tends to increase the chance of transmitter/receiver failure.
The present invention has been devised to overcome the above-outlined problems of the prior art, and an object of the invention is to provide a phase shifter comprising a wave collector and a primary radiator, and a primary radiator for use in a beam scanning antenna that uses such a phase shifter, wherein the primary radiator is constructed as a component structurally independent of a transmitter/receiver connected to it so that only the primary radiator can be moved without moving the transmitter/receiver, thereby achieving the construction of an inexpensive, high-reliability, and high-performance phase shifter and beam scanning antenna using such a primary radiator.
Another object of the invention is to provide a phase shifter that is constructed by arranging the above primary radiator and wave collector between parallel plates, and that can control the phase continuously by varying the positional relationship between the primary radiator and the wave collector.
A further object of the invention is to provide a beam scanning antenna which includes slots formed in one of parallel plates that form part of the phase shifter constructed using the above primary radiator, and which scans the beam by radiating a high-frequency signal directly through the slots after controlling the phase by the wave collector, or by feeding through the slots the high frequency signal to another antenna that is mounted outside the parallel plates.
The inventor has conducted extensive studies on the previously described problems and has found that the problems associated with the prior art can be solved by employing the following configuration.
The invention provides a primary radiator comprising:
a base part in an upper surface of which a groove having a width of xc2xd to {fraction (1/1)} of signal wavelength of a high frequency signal and a depth approximately equal to xc2xc of the signal wavelength, and whose inner wall is formed of an electrically conductive material, is formed as a waveguide for the high frequency signal; and
a moving part formed of an electrically conductive material and placed above the upper surface of the base part in such a manner as to cover the groove,
the moving part including a coupling window for an electromagnetic wave of the high frequency signal, the coupling window being positioned above the groove, and a reflecting member that is formed on a lower surface of the moving part in such a manner as to fit in a cross section of the groove and is positioned away from the coupling window by xe2x85x9 to {fraction (1/1)} of guide wavelength of the high frequency signal, and whose thickness in a longitudinal direction of the groove is not smaller than {fraction (1/10)} of the guide wavelength,
wherein the coupling window and the reflecting member are together movable along the groove in the longitudinal direction, and the electromagnetic wave of the high frequency signal propagated through the waveguide formed by the groove and the lower surface of the moving part is radiated through the coupling window.
In the invention it is preferable that a directional antenna element is mounted above the coupling window of the moving part.
In the invention it is preferable that the upper surface of the base part is made of an electrically conductive material, and a ring groove having a width of {fraction (1/8)} to xc2xd of the signal wavelength and a depth of xe2x85x9 to {fraction (1/1)} of the signal wavelength is formed in the upper surface so as to encircle the groove and be spaced apart from an opening of the groove by xc2xc to {fraction (1/1)} of the signal wavelength.
In the invention it is preferable that a plurality of the ring grooves are formed at pitches of xc2xc to {fraction (1/1)} of the signal wavelength, the innermost ring groove being spaced apart from the opening of the groove by xc2xc to {fraction (1/1)} of the signal wavelength.
In the invention it is preferable that a traverse groove having a width of xe2x85x9 to xc2xd of the guide wavelength and a depth of {fraction (1/100)} to xc2xd of the guide wavelength, and extending in a direction intersecting the longitudinal direction of the groove, is formed in a lower surface of the reflecting member.
In the invention it is preferable that a plurality of the traverse grooves are formed at pitches of xe2x85x9 to {fraction (3/2)} of the guide wavelength.
In the invention it is preferable that the reflecting member is formed at a position spaced about xc2xc or about xc2xe of the guide wavelength of the high frequency signal away from the coupling window in the lower surface of the moving part.
In the invention it is preferable that the directional antenna has a short circuited end and an open end, and is mounted so that the coupling window is located at a position spaced about xe2x85x9 to {fraction (1/1)} of the guide wavelength away from the short circuited end.
In the invention it is preferable that the directional antenna is mounted so that the coupling window is located at a position spaced about xc2xc or about xc2xe of the guide wavelength away from the short circuited end.
The invention provides a phase shifter comprising: two metal plates arranged in parallel to each other; the primary radiator of the above-described configuration placed between the metal plates; and a wave collector placed between the metal plates, and wherein: the phase of the electromagnetic wave of the high frequency signal emitted through the coupling window and converted by the wave collector is varied by varying the position of the coupling window of the primary radiator relative to the wave collector.
The invention provides a beam scanning antenna comprising: a plurality of slots, formed in one of the metal plates of the phase shifter of the above-described configuration, for coupling the electromagnetic wave to and from the wave collector, wherein a beam direction of the electromagnetic wave to be radiated from the slots is made variable.
In the invention it is preferable that a directional antenna element is mounted above the slots and the phase-controlled high frequency signal is fed to the antenna element.
First, the high frequency signal waveguide, a component of the primary radiator, is constructed using a base part, such as a cabinet, that has a groove whose inner wall is a conductor, and preferably has a conductive surface encircling the groove and conducting to the inner wall conductor of the groove, and a moving part, such as a flat plate, at least whose portion that completely covers the groove is a conductor. The groove has a width of xc2xd to {fraction (1/1)} of the signal wavelength xcexo of the high frequency signal in free space, and a depth of about xc2xc of the signal wavelength xcexo.
The moving part is provided with a coupling window for coupling the electromagnetic wave of the high frequency signal between the waveguide and the outside of the flat plate of the moving part by passing through the flat plate. The moving part is also provided with a reflecting member, such as a reflecting plate, that fits in the groove in such a manner as to close the cross section of the groove forming the waveguide, and that reflects the high frequency signal that has not been radiated outside through the coupling window but propagated through the waveguide. The size of the reflecting member is slightly smaller than the cross sectional size of the groove, to allow the reflecting member to move along the groove with the movement of the moving part; the thickness of the reflecting member is not smaller than {fraction (1/10)} of the guide wavelength xcexg of the high frequency signal, and the distance between the coupling window and the reflecting member is chosen to be equal to an appropriate one of the values falling within the range of xe2x85x9 to {fraction (1/1)} of the guide wavelength xcexg of the high frequency signal in the waveguide.
The primary radiator can thus radiate the electromagnetic wave of the high frequency signal through the coupling window while moving the coupling window and reflecting member along the waveguide.
Preferably, a waveguide antenna, for example, is mounted above the portion corresponding to the outside of the coupling window, and is made movable together with the moving part. By coupling the waveguide to the waveguide antenna via the coupling window of the moving part, the primary radiator can radiate the high frequency signal while moving the waveguide antenna.
Since the high frequency signal leaks through the gap between the base part and the moving part by the parallel-plate mode with zero cutoff frequency, a ring groove having a width of xe2x85x9 to xc2xd of the signal wavelength xcexo of the high frequency signal and a depth of xe2x85x9 to {fraction (1/1)} of the signal wavelength xcexo is formed in the upper surface of the base part in such a manner to encircle the waveguide groove in the gap between the base part and the moving part, the ring groove being spaced xc2xc to {fraction (1/1)} of the signal wavelength xcexo away from the opening of the groove and made to act as a choke. This structure can effectively prevent the leakage of the high frequency signal through the gap between the base part and the moving part while allowing the moving part to move along the upper surface of the base part.
Furthermore, since the high frequency signal leaks through the gap between the base part and the moving part by the parallel-plate mode with zero cutoff frequency, it is effective to provide one or more ring grooves as a choke in such a manner as to encircle the waveguide groove by multiple ring grooves; as the number of ring grooves is increased, the function of the choke for preventing the leakage of the high frequency signal is enhanced. In this case, the multiple ring grooves should be formed at pitches of xc2xc to {fraction (1/1)} of the signal wavelength xcexo.
Preferably, for the reflecting member also, a groove having a width of xe2x85x9 to xc2xd of the guide wavelength xcexg and a depth of {fraction (1/100)} to xc2xd the guide wavelength xcexg, and traversing the reflecting member in a direction intersecting the longitudinal direction of the waveguide groove, is formed in the lower surface of the reflecting member that faces the bottom surface of the waveguide groove. It is also preferable to form a plurality of such traverse grooves at pitches of xe2x85x9 to {fraction (3/2)} of the guide wavelength xcexg. When such traverse grooves are formed, and the sum of the depth of the traverse groove and the distance from the traverse groove to the end face of the reflecting member is set equal to xe2x85x9 to {fraction (3/2)} of the guide wavelength xcexg, the end face of the reflecting member can provide an electrical short circuiting condition with respect to the waveguide, though the end face of the reflecting member is not physically short circuited to the waveguide, and this serves to effectively prevent the high frequency signal from leaking through the reflecting member.
Then, by placing the primary radiator and flat plate-like wave collector of the above configuration between the parallel plates consisting of two metal plates arranged in parallel to each other, the phase shifter can be constructed that can vary the phase of the high frequency electromagnetic wave signal that has been radiated as a spherical wave from the coupling window of the primary radiator and converted into a plane wave by the wave collector.
Further, when a plurality of slots for coupling electromagnetic waves to and from the wave collector is formed in one of the parallel plates in the structure comprising the primary radiator and wave collector of the above configuration placed between the parallel plates, then by feeding power to the slots the high frequency electromagnetic wave signal can be radiated directly from the slots while varying the radiating direction of the electromagnetic wave beam, and the structure can thus be made to function as a beam scanning antenna. Furthermore, another directional antenna element may be mounted above the slots on the outside of the parallel plate; in this case, by feeding the phase controlled high frequency signal to this antenna element, the antenna element can be made to function as a beam scanning antenna.
As described in detail above, according to the primary radiator of the invention, the high frequency signal waveguide is constructed using the base part, in which is formed the groove whose inner wall is formed of a conductor, and the moving part, which is placed over the upper surface of the base part in such a manner as to cover the groove, and which includes the coupling window formed above the groove and the reflecting member formed in a prescribed position in such a manner as to close the cross section of the groove, and the high frequency electromagnetic wave signal propagated through the waveguide formed by the groove and the lower surface of the moving part is radiated from the coupling window while the coupling window and reflecting member are being moved along the groove in the longitudinal direction thereof; therefore, the primary radiator can be made structurally independent of the transmitter/receiver connected to it, allowing only the primary radiator to be moved without moving the transmitter/receiver, and an inexpensive, high-reliability, and high-performance phase shifter and beam scanning antenna can be constructed using the primary radiator of the above structure.
Furthermore, by forming a prescribed ring groove encircling the opening of the groove in the upper surface of the base part, or by forming a prescribed traverse groove in the lower surface of the reflecting member, a high efficiency primary radiator substantially free from high frequency signal leakage can be achieved.
Further, according to the phase shifter of the invention, the primary radiator and flat plate-like of the invention are placed between the two metal plates arranged in parallel to each other, and the phase of the high frequency electromagnetic wave signal, radiated from the coupling window and converted by the wave collector, is varied by varying the position of the coupling window of the primary radiator relative to the wave collector; in this way, the phase shifter of the invention can continuously control the phase by moving the primary radiator. More specifically, by varying the positional relationship between the primary radiator and the wave collector, the tilting of the phase of the signal fed to the slots can be varied, and as a result, a phase shifter operating in the microwave or millimeter wave band and having good characteristics can be achieved using simple configuration.
Furthermore, according to the beam scanning antenna of the invention, a plurality of slots for coupling electromagnetic waves to and from the wave collector is formed in one of the metal plates of the phase shifter of the invention, and the direction of the electromagnetic wave beam radiated from the slots is made variable; accordingly, the beam scanning antenna of the invention, while moving the primary radiator, can scan the beam by radiating the high frequency signal directly from the slots after controlling the phase by the wave collector, or by feeding the high frequency signal to another antenna through the slots.